The present invention relates to improved subassemblies for a downhole drill string. More particularly, but not by way of limitation, the present invention relates to stabilizer or reamer subassemblies which allow drilling mud fluid to flow through or around the stabilizer/reamer body. The present invention may be utilized with either vertical or horizontal drilling operations. Further the invention relates to a method for retrofitting existing subassemblies to provide the flow through feature.
A drill string is used to drill a subterranean well bore. The drill string typically consists of multiple joints of drill pipe, drill collars, and a drill bit. To facilitate completion of the well, it is important that deviation from the desired drill path be closely controlled. Additional equipment has been utilized to stabilize the drill string. These devices are commonly known as stabilizers. Sometimes it is necessary to slightly enlarge or clean an existing well bore or casing. These devices are called reamers or scrapers. These tools have a larger outside diameter than the drill collars and are in constant rotational contact with the sidewall of the well bore during the drilling process.
The problem with stabilizers/reamers/scrapers is that the contact between the device and the well bore can create conditions whereby penetrated, soft formations may collapse or swell inwardly after penetration of the bit. This may cause the device to become stuck. Sometimes water loss in some formations may cause excessive mud cake buildup on the wall of the well bore which results in sticking at the device. Formation fracturing may occur from debris packing off at the subassembly and from increased hydraulic pressure from the restricted flow of drilling fluid at the pack-off site. Packing-off may also contribute to interrupted weight on the drill bit.
Sometimes reamers which are cutting a larger bore above the drill bit bore become lodged in the walls of the formation, slowing down or stopping the drilling process. Occasionally, a casing scraper used to clean an in-place casing run also becomes stuck within the casing. These problems are tremendously costly to correct with current technology. Often the drill string must be left in the well bore and the well bore redrilled.
Thus, there is a need to provide a fluid flow through path or bypass around a packed-off or stuck subassembly. The present invention and method provide such a bypass and solves the problems associated with packing-off around the subassembly.